There’s a good reason not to get too excited about Tuesday’s report from Standard & Poor’s on the Case-Shiller home price index: As sure as the sun comes up in the morning, home prices will rise in April.

The latest Case-Shiller report said that home prices on a non-seasonally adjusted basis gained for the first time in eight months. On a monthly basis, it did the same in 2009 and 2010 — and both times it raised hopes that home prices would hit bottom “later this year.”

After accounting for seasonal factors (more homes tend to sell in April versus March), the index was virtually unchanged from April.

That’s less exciting, but it’s still good news. It means that home price declines are moderating. Consider: Prices fell by 0.1% in April; 0.3% in March, February and January; 0.4% in December; 0.5% in November; a nearly 1% in October. In addition to normal seasonal factors, such as warmer weather, home price indexes such as Case-Shiller, which measure repeat transactions of existing homes, can be skewed by the share of distressed home sales.

In fact, they may be telling us more about the share of distressed sales in certain markets than they are about where home prices are actually headed. CoreLogic Inc. produces two indexes, one that tracks all home prices and one that excludes distressed sales. It shows that all home sales continue to report substantial year-over-year declines, but non-distressed home sales aren’t reporting negative prices.

“I don’t think anyone really knows how much the index is skewed by the fact that a large portion of the transactions are distressed sales,” says Patrick Newport, an IHS Global Insight economist.

What Tuesday’s report suggests is that “some of the declines we saw in the winter were overstated. We’re now going to see a bounce,” says Thomas Lawler, an independent housing economist in Leesburg, Va.

“There’s no evidence yet that we’re in any material rebound,” he says, before making a bold prediction: “We will be in one next year.”

His reason? By the end of 2011, he estimates that housing markets will have sopped up enough of the excess vacant housing inventory so that more traditional demand and supply dynamics will be able to manage any additional foreclosures.

So what about the current weakness in housing demand? Mr. Lawler concedes that disappointing housing demand this spread “gives me a little bit of pause,” but he chalks it up to the fact that “we had a lot of stuff going on” with high gas prices, Japan’s nuclear plant and quake related disruptions, and the turmoil over the Euro.

Mr. Newport expects prices to fall by another 5% over the next year, but he says “you could quite possibly argue that [prices] are nearing a bottom, and that they may not drop another 5%.”